Process for forming a crystalline diamond film

Abstract

A crystalline diamond film is formed on a thin substrate. Energy is applied by a thermal plasma torch to a gas mixture to deposit carbon particles onto the substrate. The substrate is positioned on a pedestal with a cooling facility in which an intermediate layer of thermally conductive powder is interposed between the substrate and the pedestal.

What is claimed is: 
     
       1. A crystalline diamond film forming process comprising the steps of: arranging a pedestal cooled with cooling facility during the film forming process;   positioning a thin substrate on said pedestal with an intermediate layer which is interposed between the pedestal and the substrate, the intermediate layer comprising a thermally conductive powder;   feeding a mixture of gas composed of argon, a hydrocarbon, and hydrogen to a thermal plasma generating means; and   applying energy to the gas mixture via said thermal plasma generating means to produce decomposed carbon particles and depositing the carbon particles onto the substrate to form a crystalline diamond film.   
     
     
       2. The process according to claim 1, wherein said energy applying and carbon particle depositing step is implemented by a plasma torch gun for generating a thermal plasma to which the gas mixture is fed. 
     
     
       3. The process according to claim 1, wherein said intermediate layer comprises ceramic powders. 
     
     
       4. The process according to claim 1, wherein the thickness of the substrate is below 40 microns. 
     
     
       5. The process according to claim 1, wherein the substrate is an acoustic diaphragm. 
     
     
       6. The process according to claim 1, wherein the substrate is made of titanium. 
     
     
       7. The process according to claim 1, wherein the temperature on the substrate surface is in the range of 800 to 1000 degrees centigrade. 
     
     
       8. The process according to claim 1, wherein the gas mixture comprises Argon, Methane and Hydrogen, the mixture ratio of which is 100:0.1:7. 
     
     
       9. The process according to claim 1, wherein the material of the thermal conductive powder is selected from the group consisting of diamond, cubic boron nitride and silicon carbide. 
     
     
       10. The process according to claim 1, wherein the material of the thermal conductive powder has a melting point in excess of 1500 degrees centigrade and a thermal conductivity equal to or greater than that of the pedestal. 
     
     
       11. The process according to claim 1, wherein said energy applied to said gas mixture is thermal energy. 
     
     
       12. A crystalline diamond film forming process comprising the steps of: arranging a pedestal;   positioning a thin substrate on said pedestal with an intermediate layer which is interposed between the pedestal and the substrate, the intermediate layer comprising a thermally conductive powder;   feeding a mixture of gas composed of argon, a hydrocarbon, and hydrogen to a thermal plasma generating means;   applying energy to the gas mixture via said thermal plasma generating means to produce decomposed carbon particles and depositing the carbon particles onto the substrate to form a crystalline diamond film; and   cooling said pedestal so that the temperature on the substrate surface is maintained in the rang of 800 to 1000 degrees centigrade.   
     
     
       13. The process according to claim 12, wherein said substrate is made of titanium. 
     
     
       14. The process according to claim 12, wherein said energy applying and carbon particle depositing step is implemented by a plasma torch gun for generating a thermal plasma to which the gas mixture is fed. 
     
     
       15. The process according to claim 12, wherein said substrate is an acoustic diaphragm. 
     
     
       16. The process according to claim 12, wherein said energy applied to said gas mixture is thermal energy. 
     
     
       17. The process according to claim 12, wherein the material of said thermal conductive powder is selected from the group consisitng of diamond, cubic boron nitride and silicon carbide.